Arrangement for a direct drive generator for a wind turbine and method for the assembly of the generator

ABSTRACT

The invention concerns an arrangement for a direct drive generator for a wind turbine, which generator comprises a stator with several stator segments each stator segment having at least one stator element for the power generation and which generator comprises a rotor pivotable around a center axis of the generator and relatively to the stator with several rotor segments each rotor segment having at least one rotor element for the power generation, wherein said arrangement comprises at least one stator segment and at least one rotor segment, and wherein the at least one stator segment and the at least one rotor segment are able to be at least temporarily supported against each other. The invention concerns further a direct drive generator comprising such an arrangement, a wind turbine comprising such a direct drive generator as well as a method for the assembly of the direct drive generator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European application No. 07022883.8filed Nov. 26, 2007, which is incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The invention relates to an arrangement for a direct drive generator, adirect drive or directly driven generator comprising the arrangement, awind turbine comprising a direct drive generator as well as to a methodfor the assembly of a direct drive generator.

BACKGROUND OF THE INVENTION

In principle there are two main types of wind turbines in view of thedrive configuration of a wind turbine. The first type of a wind turbineis the more classical type of a wind turbine comprising a gearboxarranged between a main shaft and a generator of the wind turbine. Thesecond type of a wind turbine is a gearless type, whereat the gearboxand the conventional generator are substituted by a multipolargenerator, a so called direct drive or directly driven generator. Such adirect drive generator can be made as a synchronous generator withwinded rotor or with permanent magnets attached to the rotor, or it canbe designed as an alternative type of a generator.

Common to direct driven generators is that their physical dimensions arerelatively large. At a typical air gap diameter of approximately 5 m fora multi-megawatt direct drive generator the outer diameter is on theorder of approximately 6 m or even more. The large outer diameter makesthe transport of the direct drive generator difficultly and the heavydead load of the direct drive generator involves further difficultiese.g. concerning the replacement for repair by occurred breakdowns.

A further difficulty arises in the normal configuration of a windturbine with a direct drive generator, where the direct drive generatoris arranged between the wind turbine rotor and the tower in order toyield a compact machine construction. In this case it will be necessaryto dismantle the whole wind turbine rotor by a required dismantling ofthe direct drive generator.

To overcome these problems at least partially there were somesuggestions to divide parts of the generator.

In WO 98/20595 A1 a stator for a rotating electric machine is disclosedcomprising a stator core and a winding. The stator core is provided withstator teeth extending radially inwards towards a rotor. Each statortooth is configured as a number of tooth sections joined axially into astator tooth plank. That stator tooth planks are fitted together side byside thus forming a section of the stator core. This construction makesthe transport of parts of the rotating electric machine to the site oferection partially easier, because the stator can be assembled on site.However, this construction requires a stator housing as such havingrelatively large outer dimensions.

From U.S. Pat. No. 4,594,552 an armature winding of a split stator isknown. The split stator has a slotted core divided by at least twocircumferentially-spaced split lines to facilitate the assembly and thedisassembly of the split stator. The armature winding comprises armaturecoils in the slots of the stator core connected to provide poles andarranged to provide a plurality of armature coils divided at the splitlines. Connecting and disconnecting means are provided to connect anddisconnect the armature coils when the split stator is assembled anddisassembled, respectively. This construction, however, also requires astator housing as such having relatively large outer dimensions.

U.S. Pat. No. 5,844,341 describes an electric generator to be driven bya low speed device such as wind turbine. The generator consists of oneor more rotor rings of many permanent magnets of alternating polarityand coaxial stator rings of many laminated yokes, each yoke definingslots to locate coils. The yokes and coils form modules which aresupported by beams relatively to the rotor rings. The drawback of thisconfiguration is that the electromechanical properties in this form ofmodular construction with single polar pairs separated by air gaps maybe disadvantageous, and that a possible dismantling of a single statormodule can involve that the whole generator has to be opened in situimplying risk of humidity, dirt etc., and that it may be cumbersome ifthe stator module has to be taken out in a disadvantageous direction.

U.S. Pat. No. 6,781,276 B1 describes a generator for a wind turbinecomprising a stator and a rotor. The stator has a number of statormodules that are individual and which may be installed, repaired anddismantled individually and independently of each other. This generatorhas no part larger than the air gap diameter. But even if no part islarger than the air gap diameter, the largest element to be transportedstill has a substantial size, given that the rotor is a single piece. Inits completed form this rotor is fitted with strong permanent magnetsand needs to be covered by a nonmagnetic layer, e.g. wood or polystyreneof a certain thickness during transportation, and while the dimensionsof the rotor are smaller than the dimensions of the finished generator,it is still at maybe 5 m diameter and 1.5 m length a very substantialpiece of equipment to transport.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anarrangement for a direct drive generator and a generator as initiallymentioned in such a way, that in particular the transport of thegenerator to the site of erection is simplified. It is a further objectof the invention to indicate a wind turbine comprising a respectivegenerator as well as a method for the assembly of the generator of thewind turbine.

This object is inventively achieved by an arrangement for a direct driveor directly driven generator for a wind turbine, which generatorcomprises a stator with several stator segments each stator segmenthaving at least one stator element operative for the electrical powergeneration and which generator comprises a rotor rotatable around acenter axis of the generator and relatively to the stator with severalrotor segments each rotor segment having at least one rotor elementoperative for the electrical power generation, wherein said arrangementcomprises at least one stator segment and at least one rotor segment,and wherein the at least one stator segment and the at least one rotorsegment are able to be at least temporarily supported against eachother. According to the invention the direct drive generator is asegmented generator with stator segments and rotor segments building atleast a part of the generator. These segments are in principle singlemanageable parts. However in practice the handling of the statorsegments and of the rotor segments can be difficult in particular whene.g. a stator element of a stator segment comprises a winding form witha winding and a rotor element of a rotor segment comprises a permanentmagnet with a large magnetic pull. Therefore an arrangement comprisingat least one stator segment and at least one rotor segment is suggestedwherein the stator segment and the rotor segment are able to be at leasttemporarily supported against each other e.g. during the transport ofthe arrangement. Thereby the stator element for the power generation andthe rotor element for the power generation are arranged oppositely toeach other wherein an air gap remains between the stator element for thepower generation and the rotor element for the power generation. Sincein this way the magnetic circuits concerning the stator element and therotor element for the power generation are closed, normally no specificprotection of the arrangement against undesired magnetic pull is needed,in particular when the generator comprises permanent magnets. As aconsequence the transportation of the arrangement comprising a statorsegment and a rotor segment which are supported against each other issimplified in comparison to the transport of single stator or rotorsegments. Further on, since during assembly and disassembly of thegenerator a rotor segment is allowed to rest on a stator segment, anycrane lift is as a rule disconnected from magnetic pull. Therefore thetransport, assembly and disassembly of a generator are simplified.

Preferably the at least one stator segment comprises at least one firstsupporting projection and the at least one rotor segment comprises atleast one second supporting projection, wherein the first supportingprojection of the at least one stator segment and the second supportingprojection of the at least one rotor segment are able to be at leasttemporarily supported against each other. By means of the supportingprojections a rotor segment is able to rest on stator segment inparticular when the generator particularly the arrangements for thegenerator comprising a stator segment and a rotor segment supportedagainst each other are transported, assembled or disassembled.

Therefore according to an embodiment of the invention the at least onestator segment and the at least one rotor segment of an arrangement areable to build at least temporarily a stator/rotor segment unit.

In a further embodiment of the invention the at least one rotor segmentis at least partially arranged inside the at least one stator segment.In this way a compact arrangement is achieved.

According to a variant of the invention the at least one stator segmentis a ring-segment-shaped stator segment and/or the at least one rotorsegment is a ring-segment-shaped rotor segment. In the assembled statusthe ring-segment-shaped stator segments build a stator ring and thering-segment-shaped rotor segments build a rotor ring substantiallyarranged inside the stator ring.

In a variant of the invention the at least one ring-segment-shapedstator segment comprises an exterior, ring-segment-shaped statorsupporting element, a radially inwardly directed frontring-segment-shaped stator connection element arranged on the front sideof the exterior, ring-segment-shaped stator supporting element and aradially inwardly directed rear ring-segment-shaped stator connectionelement arranged on the rear side of the exterior, ring-segment-shapedstator supporting element for establishing a inwardly open,substantially U-shaped ring-segment-shaped stator segment, wherein atleast one stator element is arranged on the inside of the exteriorring-segment-shaped stator supporting element. Thereby the expressionsubstantially U-shaped shall also cover other comparable forms such asV-shaped etc.

In a comparable way the at least one ring-segment-shaped rotor segmentcomprises an exterior, ring-segment-shaped rotor supporting element, aradially inwardly directed front ring-segment-shaped rotor connectionelement arranged on the front side of the exterior, ring-segment-shapedrotor supporting element and a radially inwardly directed rearring-segment-shaped rotor connection element arranged on the rear sideof the exterior, ring-segment-shaped rotor supporting element forestablishing a inwardly open, substantially U-shaped ring-segment-shapedrotor segment, wherein at least one rotor element is arranged on theoutside of the exterior ring-segment-shaped rotor supporting element.Thereby the expression substantially U-shaped shall again also coverother comparable forms such as V-shaped etc.

According to a further variant of the invention each ring-segment-shapedstator connection element of the ring-segment-shaped stator segmentcomprises at least one first supporting projection and eachring-segment-shaped rotor connection element of the ring-segment-shapedrotor segment comprises at least one second supporting projection.

The further object of the invention is achieved by a direct drive ordirectly driven generator for a wind turbine comprising at least onearrangement as disclosed afore. Typically the generator comprisesseveral arrangements for establishing the mentioned stator ring and thementioned rotor ring.

According to an embodiment of the invention the generator comprises afront and a rear ring-shaped supporting element of the stator to whichring-shaped supporting elements of the stator several stator segments ofseveral arrangements are attached in a non-destructively detachable way.Preferably the front and the rear ring-shaped supporting elements of thestator are ring-shaped end plates of the stator. As a rule thering-shaped end plates of the stator are one piece elements ensuringparticularly a sufficient roundness.

In a further embodiment of the invention the generator comprises a frontand a rear ring-shaped supporting element of the rotor to whichring-shaped supporting elements of the rotor several rotor segments ofseveral arrangements are attached in a non-destructively detachable way.As in case of the stator the front and the rear ring-shaped supportingelements of the rotor are preferably ring-shaped end plates of therotor. As a rule the ring-shaped end plates of the rotor are one pieceelements ensuring particularly a sufficient roundness.

In a further development of the invention the junctions between thefront and the rear ring-shaped supporting elements of the stator and thestator segments and/or the junctions between the front and the rearring-shaped supporting elements of the rotor and the rotor segments arelocated substantially at a radius in relation to the center axis of thegenerator which is equal or smaller than the radius of an air gapbetween the stator elements and the rotor elements. Thus the ring-shapedsupporting elements of the stator and the rotor have dimensions inparticular diameters, which are preferably significantly smaller thanthe air gap diameter of the generator. In this way the transport of thering-shaped supporting elements of the stator and the rotor, theassembly and the disassembly of the stator and the rotor and thegenerator respectively on the site of erection are simplified.

In case of a wind turbine not the whole mounted generator has to becarried into the nacelle using e.g. a crane. In fact the significantlylighter single manageable parts, arrangements and/or segments of thegenerator are able to be carried into the nacelle where the generator isable to be assembled, repaired or disassembled.

According to a variant of the invention the width of the air gap betweenthe stator elements and the rotor elements is adjustable. Preferably thejunctions between the ring-shaped supporting elements of the stator andthe stator segments and/or the junctions between the ring-shapedsupporting elements of the rotor and the rotor segments compriseadjusting means for the adjustment of the width of the air gap.According to an embodiment of the invention the adjusting means compriseat least one shim.

According to a further embodiment of the invention a stator segmentcomprises at least one winding form with a winding as a stator elementand/or a rotor segment comprises at least one permanent magnet as arotor element.

In an embodiment of the invention the stator segments and thering-shaped supporting elements of the stator and/or the rotor segmentsand the ring-shaped supporting elements of the rotor comprise axialand/or radial extending flanges for the mounting. Thereby the axialextending flanges extend preferably substantially in the directions ofthe center axis A of the main shaft and the radial extending flangesextend preferably substantially perpendicularly in relation to thecenter axis A of the main shaft. In this way the stator and rotorsegments can be comparatively simply attached to the respectivering-shaped supporting elements.

According to a further embodiment of the invention at least one of thering-shaped supporting elements of the rotor and/or at least one of thering-shaped supporting elements of the stator comprise at least one manhole for providing access to the internals of the generator. Thus atleast one of the front or rear ring-shaped supporting elements can haveone or more man holes which are preferably closable.

The third object of the invention is achieved by a wind turbinecomprising at least one arrangement as disclosed afore and/or agenerator as disclosed afore.

The object concerning the method is achieved by a method for theassembly of a generator using afore disclosed arrangements, wherein

-   respectively at least one rotor segment and respectively at least    one stator segment are supported against each other for building a    combined stator/rotor segment unit,-   several stator/rotor segment units are transported to the site of    erection of the wind turbine,-   each stator/rotor segment unit is arranged on the ring-shaped    supporting elements of the stator and on the ring-shaped supporting    elements of the rotor, wherein each stator segment of each    stator/rotor segment unit is arranged on the ring-shaped supporting    elements of the stator and each rotor segment of each stator/rotor    segment unit is arranged on the ring-shaped supporting elements of    the rotor. As disclosed afore by building a stator/rotor segment    unit wherein preferably a rotor segment rests on a stator segment    the magnetic circuits are closed so that the transport is    simplified.

According to a variant of the invention first each stator segment of astator/rotor segment unit is attached to the ring-shaped supportingelements of the stator and then each rotor segment of a stator/rotorsegment unit is attached to the ring-shaped supporting elements of therotor for pulling away each rotor segment from its supporting position.

In a further development of the invention the radial position of astator segment is adjusted by means of adjusting means arranged betweenthe ring-shaped supporting elements of the stator and the respectivestator segment and/or the radial position of a rotor segment is adjustedby means of adjusting means arranged between the ring-shaped supportingelements of the rotor and the respective rotor segment. Thus the desiredor required width of the air gap between the stator and rotor elementsfor the power generation can be adjusted in a relatively simple way.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be explained in more detail withreference to the schematic drawings, wherein

FIG. 1 shows a part of an inventive wind turbine,

FIG. 2 shows in an enlarged illustration the main shaft and a part ofthe direct drive generator of the wind turbine of FIG. 1,

FIG. 3 shows in an enlarged illustration a part of the direct drivegenerator of the wind turbine of FIG. 1, and

FIG. 4 shows the view of the generator of the wind turbine of FIG. 1 inthe direction of the arrows IV of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically a first embodiment of an inventive windturbine 1 comprising an inventive direct drive or directly drivengenerator 2 which is arranged on the upwind side of a tower 3 of thewind turbine 1.

A tower flange 4 is arranged on the top of the tower 3. A retainingarrangement is arranged on the tower flange 4 comprising in case of thepresent embodiment of the invention a bedplate 5, a retaining frame inform of a retaining arm 6 and a stationary or fixed hollow shaft 7. Thebedplate 5 is attached to the tower flange 4. The wind turbine 1comprises in a not explicitly shown manner a yaw system for turning thebedplate 5 of the wind turbine 1 around the centre axis Y of the tower 3together with the other components of the wind turbine 1 which aredirectly or indirectly attached to the bedplate 5.

The retaining arm 6 is on its base side directly arranged on thebedplate 5. On the other side the retaining arm 6 comprises a flange 8.The stationary shaft 7 is attached to the flange 8 with a flange 9. Thering-shaped flange 8 of the retaining arm 6 and the ring-shaped flange 9of the stationary shaft 7 are bolted together with a plurality of boltsarranged around the ring shaped flanges.

A main shaft 10 or a main rotor pipe 10 is pivoted on the stationaryshaft 7 by means of a first main bearing 11 and a second main bearing12. Each main bearing 11, 12 supported by the stationary shaft 7comprises an inner and an outer bearing shell. The inner bearing shellsof the both main bearings 11, 12 are mounted on the stationary shaft 7,whilst the outer bearing shells of the both main bearings 11, 12 arefitted inside the main shaft 10.

On the front end the main shaft 10 comprises a ring-shaped flange 13.The ring-shaped flange 13 is firmly, but detachably connected to a hub14 of the wind turbine 1. The hub 14 comprises three mounting devices 15for three not explicitly shown, but well known wind rotor blades.

In case of the present embodiment of the invention the mentioned directdrive or directly driven generator 2 is substantially arranged aroundthe main shaft 10. The direct drive generator 2 comprises a rotor 16 ora rotor arrangement 16 and a stator 17 or a stator arrangement 17.

The rotor 16 comprises in case of the present embodiment of theinvention a first supporting element 18 in form of a front ring-shapedrotor end plate 18, a second supporting element 19 in form of a rearring-shaped rotor end plate 19 and a plurality of ring-segment-shapedrotor segments 20 attached to the front ring-shaped rotor end plate 18and the rear ring-shaped rotor end plate 19. In case of the presentembodiment of the invention the rotor 16 comprises sixring-segment-shaped rotor segments 20 building a rotor ring when the sixring-segment-shaped rotor segments 20 are attached to the preferablyone-piece front and rear ring-shaped rotor end plates 18, 19.

The stator 17 comprises in case of the present embodiment of theinvention a first supporting element 26 in form of a front ring-shapedstator end plate 26, a second supporting element 27 in form of a rearring-shaped stator end plate 27 and a plurality of ring-segment-shapedstator segments 28 attached to the front ring-shaped stator end plate 26and the rear ring-shaped stator end plate 27. In case of the presentembodiment of the invention the stator 17 comprises also sixring-segment-shaped stator segments 28 (cp. FIG. 4) building a statorring when the six ring-segment-shaped stator segments 28 are attached tothe preferably one-piece front and rear ring-shaped stator end plates26, 27.

In case of the present embodiment of the invention thering-segment-shaped stator segments 28 and the ring-segment-shaped rotorsegments 20 are designed in such a way that the junctions 50, 51 betweenthe ring-shaped stator end plates 26, 27 and the ring-segment-shapedstator segments 28 as well as the junctions 52, 53 between thering-shaped rotor end plates 18, 19 and the ring-segment-shaped rotorsegments 20 are located substantially at a radius R1 in relation to acentre axis A of the generator 2 which is smaller than the radius R2 ofthe air gap 34 between stator elements 33 for the power generationarranged on the ring-segment-shaped stator segments 28 and rotorelements 25 for the power generation arranged on the ring-segment-shapedrotor segments 20. Thus in case of the present embodiment of theinvention the maximum diameters of the ring-shaped stator and rotor endplates are 2*R1. These diameters are significantly smaller than thediameter of the air gap 34 (2*R2). This simplifies the transport of thering-shaped stator and rotor end plates.

A ring-segment-shaped rotor segment 20 comprises an exterior,ring-segment-shaped rotor supporting element 54, a radially inwardlydirected front ring-segment-shaped rotor connection element 55 arrangedon the front side of the exterior, ring-segment-shaped rotor supportingelement 54 and a radially inwardly directed rear ring-segment-shapedrotor connection element 56 arranged on the rear side of the exterior,ring-segment-shaped rotor supporting element 54 for establishing aninwardly open, substantially U-shaped ring-segment-shaped rotor segment20, wherein at least one rotor element 25 in form of at least onepermanent magnet 25 is arranged on the outside of the exteriorring-segment-shaped rotor supporting element 54. Thereby aring-segment-shaped rotor segment 20 connects the front and the rearring-shaped rotor end plates 18, 19 with each other.

As shown in FIG. 2 and FIG. 3 a front ring-segment-shaped rotorconnection element 55 comprises on its end a ring-segment-shaped flange21 and a ring-segment-shaped supporting projection 57. A rearring-segment-shaped rotor connection element 56 comprises on its end aring-segment-shaped flange 22 and a ring-segment-shaped supportingprojection 58. The front ring-shaped rotor end plate 18 has aring-shaped flange 23 and the rear ring-shaped rotor end plate 19 has aring-shaped flange 24. In case of the present embodiment of theinvention the flanges 21 and 23 as well as the flanges 22 and 24 arebolted together to build up the rotor 16. In the described way allring-segment-shaped rotor segments 20 are attached to the front and therear ring-shaped end plates 18, 19. Thus the rotor 16 has substantiallya hollow-cylindrical shape.

In a comparable way a ring-segment-shaped stator segment 28 comprises anexterior, ring-segment-shaped stator supporting element 67, a radiallyinwardly directed front ring-segment-shaped stator connection element 68arranged on the front side of the exterior, ring-segment-shaped statorsupporting element 67 and a radially inwardly directed rearring-segment-shaped stator connection element 69 arranged on the rearside of the exterior, ring-segment-shaped stator supporting element 67for establishing an inwardly open, substantially U-shaped,ring-segment-shaped stator segment, wherein at least one stator element33 in form of a winding form 75 with a winding 76 is arranged on theinside of the exterior ring-segment-shaped stator supporting element 67.Thereby a ring-segment-shaped stator segment 28 connects the front andthe rear ring-shaped stator end plates 26, 27 with each other.

As shown in FIG. 2 and FIG. 3 a front ring-segment-shaped statorconnection element 68 comprises on its end a ring-segment-shaped flange29 and a ring-segment-shaped supporting projection 60. A rearring-segment-shaped stator connection element 69 comprises on its end aring-segment-shaped flange 30 and a ring-segment-shaped supportingprojection 61. The front ring-shaped stator end plate 26 has aring-shaped flange 31 and the rear ring-shaped stator end plate 27 has aring-shaped flange 32. In case of the present embodiment of theinvention the flanges 29 and 31 as well as the flanges 30 and 32 arebolted together to build up the stator 17. In the described way allring-segment-shaped stator segments 28 are attached to the front and therear ring-shaped stator end plates 26, 27. Thus also the stator 17 hassubstantially a hollow-cylindrical shape.

In case of the present embodiment of the invention eachring-segment-shaped rotor segment 20 is substantially arranged inside aring-segment-shaped stator segment 28. In particular during thetransport, the assembly and the disassembly of the ring-segment-shapedstator and rotor segments 20, 28 one ring-segment-shaped stator segment28 and one ring-segment-shaped rotor segment 20 are able to build anarrangement, more precisely a stator/rotor segment unit. Thereby thering-segment-shaped rotor segment 20 is moved into thering-segment-shaped stator segment 28 until the ring-segment-shapedrotor segment 20 rests on the ring-segment-shaped stator segment 28.More precisely the projections 57, 58, 60, 61 engage, whereat thesupporting projection 60 and the supporting projection 57 as well as thesupporting projection 61 and the supporting projection 58 are supportedagainst each other. In general the projections 57, 58, 60, 61 engage ifthe air gap between the stator elements and the rotor elements for thepower generation is reduced to a value a certain level below the nominalvalue of the air gap. The magnetic pull during the mounting of thestator/rotor segment unit is counteracted by suitable tools, e.g. a setof jacks. Once the projections 57, 58, 60, 61 engage, the magnetic pullis taken by the projections and the suitable tools can be removed. Inthis position the magnetic circuits are as a rule closed and thestator/rotor segment unit no longer poses any risk in relation to thestrong permanent magnets. The stator/rotor segment unit is able to betransported, assembled and disassembled with no special precautions.

On the site of erection of the wind turbine 1 first the supportingstructures are assembled—the stationary shaft 7, the main bearings 11,12, the main shaft 10, a third and a fourth bearing 35, 36, describedlater, and the ring-shaped rotor end plates 18, 19 as well as thering-shaped stator end plates 26, 27.

For the assembly of the generator 2 a stator/rotor segment unit is, asindicated above, arranged on the front and the rear ring-shaped endplates 18, 19, 26, 27. Thereby the flange 29 of a frontring-segment-shaped stator connection element 68 and the flange 31 ofthe front ring-shaped stator end plate 26 as well as the flange 30 of arear ring-segment-shaped stator connection element 69 and the flange 32of the rear ring-shaped stator end plate 27 are bolted together withschematically shown flange bolts 62. This is done for all sixstator/rotor segment units. Any necessary adjustment of the radialposition of a ring-segment-shaped stator segment 28 is carried out withnot explicitly shown shims in the junctions 50, 51 between the flanges29, 31 as well as between the flanges 30, 32. Thereby the respectiveshims are inserted between the respective flanges and then the flangebolts 62 are inserted in respective bolt holes and tightened.

Afterwards the flanges 21 of the front ring-segment-shaped rotorconnection elements 55 and the flange 23 of the front ring-shaped rotorend plate 18 and the flanges 22 of the rear ring-segment-shaped rotorconnection elements 56 and the flange 24 of the rear ring-shaped rotorend plate 19 are bolted together with schematically shown flange bolts63. Thereby the ring-segment-shaped rotor segments 20 are as a rulepulled away from the resting position, in which the projections 57, 58,50, 61 engage. Any necessary adjustment of the radial position of aring-segment-shaped rotor segment 20 is carried out with not explicitlyshown shims in the junctions 52, 53 between the flanges 21, 23 as wellas between the flanges 22, 24 before the flange bolts 63 are inserted inrespective bolt holes and finally tightened.

If a ring-segment-shaped rotor segment 20 or a ring-segment-shapedstator segment 28 needs e.g. replacement the described steps are carriedout in reverse order and the replacement stator/rotor segment unit isassembled as described.

Based on trial rotations the radial positions of the ring-segment-shapedrotor segments 20 as well as the radial positions of thering-segment-shaped stator segments 28 are able to be fine tuned withthe shims in the junctions 50-53. Thus the width of the air gap 34between the electrical stator elements 33 of the stator 17 and thepermanent magnets 25 of the rotor 16 is able to be adjusted to establisha preferably completely uniform and concentric air gap 34.

In order that the rotor 16 can turn together with the main shaft 10around the centre axis A of the main shaft 10 and relatively to thestator 17 the wind turbine 1 in particular the direct drive generator 2comprise the already mentioned third or front generator bearing 35 andthe already mentioned fourth or rear generator bearing 36. The relativepositions of the stator 17 and the rotor 16 are maintained by the thirdand the fourth bearing 35, 36.

The third bearing 35 is in case of the present embodiment of theinvention attached to a flange 37 of the main shaft 10. More preciselythe inner bearing shell 38 of the third bearing 35 is firmly attached tothe flange 37 of the main shaft 10. The inner bearing shell 38 of thethird bearing 35 is furthermore firmly attached to the front ring-shapedrotor end plate 18, which supports the front part of the rotor 16. Theouter bearing shell 39 of the third bearing 35 is firmly connected tothe front ring-shaped stator end plate 26, which supports the front partof the stator 17.

The rear part of the stator 17 is supported by the rear ring-shapedstator end plate 27, which is firmly connected to the flange 9 of thestationary shaft 7 and thus to the retaining arrangement. In case of thepresent embodiment of the invention the inner bearing shell 40 of thefourth bearing 36 is firmly attached to the rear ring-shaped stator endplate 27 and the rear ring-shaped rotor end plate 19 supporting the rearpart of the rotor 16 is firmly connected to the outer bearing shell 41of the fourth bearing 36.

Based on the described arrangement comprising the main shaft 10, thefirst main bearing 11, the second main bearing 12, the rotor 16, thestator 17, the third bearing 35 and the fourth bearing 36 the main shaft10 turns in operation of the wind turbine 1 together with the rotor 16relatively to the stator 17.

For avoiding situations in which the four bearing arrangement isstatically undetermined in case of the present embodiment of theinvention the front ring-shaped rotor end plate 18 firmly supported onthe main shaft 10 and the rear ring-shaped stator end plate 27 firmlysupported on the retaining arrangement comprise a certain and sufficientextent of flexibility in the directions of the centre axis A of the mainshaft 10. Thereby these end plates 18, 27 act like membranes supportingthe rotor 16 and the stator 17 substantially firmly in the radialdirection so as to maintain the width of the air gap 34, but flexingreadily so as to allow e.g. a bending of the main shaft 10 with no majorresistance. In particular the end plates 18, 27 have such dimensionsthat they have a comparatively little bending stiffness. They simplyflex passively when e.g. the main shaft 10 is shifted a bit bydeflection. Thus when a bending of the main shaft 10 occurs to which therotor 16 and the stator 17 are connected the front ring-shaped rotor endplate 18 and the rear ring-shaped stator end plate 27 bend insubstantially a respective way in the directions of the centre axis Awherein the width of the air gap 34 is maintained substantially constantor within required tolerances.

As a consequence of the four bearing arrangement, in addition to theloads from the wind turbine rotor and the main shaft 10 the two mainbearings 11, 12 carry approximately half of the weight of the generator2, approximately the other half of the weight of the generator 2 isdirectly supported on the retaining arrangement. The third or frontgenerator bearing 35 carries approximately half of the weight of thestator 17, approximately the other half of the weight of the stator 17is supported on the retaining arrangement. The fourth or rear generatorbearing 36 carries approximately half of the weight of the rotor 16,approximately the other half of the weight of the rotor 16 is supportedon the main shaft 10.

Based on the described design or structure of the wind turbine 1 inparticular based on the described generator arrangement comprising thethird and fourth bearing the rotor 16 and the stator 17 are supported onboth sides, the front side and the rear side. This enables a morelightweight rotor and in particular a more lightweight statorconstruction with less dimensions of the stator structure in particularof the stator support structure like the end plates and so on tomaintain in operation of the wind turbine 1 the width of the air gap 34within the necessary tolerances along the directions of the centre axisA and around the perimeter.

Unlike to the afore described embodiment of the invention the frontring-shaped stator end plate 26 and the rear ring-shaped rotor end plate19 are able to comprise the certain extent of flexibility in thedirections of the centre axis A of the main shaft 10, whilst the frontring-shaped rotor end plate 18 and the rear ring-shaped stator end plate27 have not these flexibility. Also in this case the width of the airgap 34 is able to be held substantially constantly or at least withinrequired tolerances.

The ring-shaped rotor end plate and the ring-shaped stator endplate-which have the certain flexibility need not to have theflexibility in the whole end plates. Thus the ring-shaped end plates areable to have different areas. The respective ring-shaped rotor end platemay have e.g. a comparatively rigid area e.g. for the attachment of thethird bearing and an area having the mentioned flexibility in thedirections of the centre axis A. In the same way the respectivering-shaped stator end plate may have e.g. a comparatively rigid areae.g. for the attachment of the fourth bearing and an area having thementioned flexibility in the directions of the centre axis A.

The front ring-shaped rotor end plate is able to be directly arranged onthe main shaft. In this case the third bearing is able to be directlyattached to the main shaft or to the front ring-shaped rotor end plate.

It is not necessary to attach the fourth bearing to the rear ring-shapedstator end plate. The fourth bearing is also able to be directlyattached to the retaining arrangement e.g. the stationary shaft or theretaining frame or arm.

As a rule the ring-shaped end plates are made of an appropriate metal ormetal alloy. The ring-shaped end plates do not need to have the samediameter. In fact the different ring-shaped end plates are able to havedifferent diameters. In this case also the respectivering-segment-shaped segments have to be modified in relation to theradial extension of the radially inwardly directed ring-segment-shapedstator connection elements to build the stator or the rotor.

FIG. 4 shows the view of the generator 2 of the wind turbine 1 in thedirection of the arrows IV of FIG. 1. In FIG. 4 the third or generatorbearing 35, the front ring-shaped stator end plate 26, the flanges 29,31 and the six ring-segment-shaped stator segments 28 building thestator ring 71 are cognizable. In case of the present embodiment of theinvention the front ring-shaped stator end plate 26 comprises six manholes 70 providing access to the internals of the generator. In the sameway the other ring-shaped end plates of the stator or the rotor are ableto comprise man holes. Thereby the man holes are as a rule closed bymeans of a kind of door.

In case of the present embodiment of the invention in eachring-segment-shaped stator segment 28 a ring-segment-shaped rotorsegment 20 is substantially centrically arranged. But it is alsopossible that two or more ring-segment-shaped rotor segments 20 aresubstantially arranged in a ring-segment-shaped stator segment 28.

By the way the generator 2 is able to comprise less or morering-segment-shaped stator segment 28 building the stator ring as wellas less or more ring-segment-shaped rotor segment 20 building the rotorring as described afore. Furthermore it is not necessary that the rotorsegments or the stator segments have a ring-segment shape.

The non-destructively detachable connection between the end plates andthe ring-segment-shaped segments need not to be a bolted joint.

In case of the described embodiment of the invention thering-segment-shaped stator segments 28 and the ring-shaped stator endplates 26, 27 as well as the ring-segment-shaped rotor segments 20 andthe ring-shaped rotor end plates 18, 19 comprise axial extending flanges21-24, 29-32 for the mounting. Thereby the axial extending flanges21-24, 29-32 extend substantially in the directions of the centre axisA. But the mounting is also able to be done by radial extending flangesor other suitable means. Thereby the radial extending flanges extendsubstantially perpendicularly in relation to the centre axis A.

Unlike described before the direct drive generator is also able to bearranged on the downwind side of the tower.

By the way the wind turbines 1 comprise a housing H normally called thenacelle which contain the generator 2 and at least a part of theretaining arrangement.

The invention claimed is:
 1. An arrangement for a wind turbine,comprising: a tower of the wind turbine; a tower flange at a top of thetower; a direct drive generator arranged on an upwind side of the tower,said direct drive generator comprising: a stator, a stator segment inthe stator, a stator element in the stator segment for generating apower, a rotor rotatable around a center axis of the generator, a rotorsegment in the rotor and supported against the stator segment, and arotor element in the rotor segment for generating the power; wherein thestator segment comprises a first supporting projection; wherein therotor segment comprises a second supporting projection; wherein thefirst supporting projection and the second supporting projection aresupported against each other.
 2. The arrangement as claimed in claim 1,wherein the stator segment and the rotor segment build a stator/rotorsegment unit.
 3. The arrangement as claimed in claim 1, wherein therotor segment is arranged inside of the stator segment.
 4. Thearrangement as claimed in claim 1, wherein the stator segment isring-segment shaped such that a plurality of stator segments areprovided such that the stator is ring shaped; said generator furthercomprising a ring-shaped stator end plate with a plurality of man holesto provide access to an internal portion of the generator; and wherein arespective ring-segment shaped rotor segment is centrically arrangedwithin each of the plurality of stator segments.
 5. The arrangement asclaimed in claim 1, further comprising a retaining arm with a first sideattached to the top of the tower and a second side attached to thegenerator; said second side configured to be bolted adjacent to astationary shaft.
 6. The arrangement as claimed in claim 1, furthercomprising: a front and a rear ring-shaped supporting elements of thestator for attaching the stator segment, and a front and a rearring-shaped supporting element of the rotor for attaching the rotorsegment.
 7. The arrangement as claimed in claim 6, wherein a junctionbetween the front and the rear ring-shaped supporting elements of thestator and the stator segment or a junction between the front and therear ring-shaped supporting elements of the rotor and the rotor segmentis located substantially at a radius in relation to a center axis of thegenerator which is equal or smaller than a radius of an air gap betweenthe stator element and the rotor element.
 8. The arrangement as claimedin claim 7, wherein a width of the air gap is adjustable.
 9. Thearrangement as claimed in claim 8, wherein the junction between thering-shaped supporting elements of the stator and the stator segment orthe junction between the ring-shaped supporting elements of the rotorand the rotor segment comprises an adjusting device for adjusting thewidth of the air gap.
 10. The arrangement as claimed in claim 9, whereinthe adjusting device comprises a shim.
 11. The arrangement as claimed inclaim 6, wherein the front and the rear ring-shaped supporting elementsof the stator or the front and the rear ring-shaped supporting elementsof the rotor comprise a man hole to provide access to an internalportion of the generator.
 12. The arrangement as claimed in claim 1,wherein the stator segment comprises a winding form with a winding whichis used as the stator element, or wherein the rotor segment comprises apermanent magnet which is used as the rotor element.
 13. The arrangementas claimed in claim 1, wherein six stator segments form the ring-shapedstator and wherein six rotor segments form a ring-shaped rotor.